Pneumatic gripper

ABSTRACT

For grasping objects having a limited weight and a random shape, a pneumatic gripper is proposed, which has an approximately U-shaped support (10) and a compressed air ejection nozzle (12), mounted on one of the end branches (10b) of the support and oriented towards the intermediate branch (10a), in the vicinity of the bend (10d) connecting the latter to the other end branch (10c). Rails (22) channel the compressed air jet from the nozzle (12) to the end of the branch (10c). The object (O) is attracted by the pressure drop or vacuum formed in the vicinity of the bend (10d) and can then be raised and manipulated.

The invention relates to a pneumatic gripper more particularly designedfor use on an automaton or robot.

The grippers normally used on robots are mechanisms in the form of grabshaving at least two articulated fingers. The gripping of an object takesplace by bringing each of the fingers into contact with said object andby applying thereto an adequate force to permit its handling.

Such grippers constitute a satisfactory solution when it is wished totransport a non-fragile object. Thus, they then have the advantage ofallowing objects with an often considerable weight to be gripped.Moreover, they make it possible to apply a force to said object whenthis is necessary, e.g. for putting it into place.

However, these known grippers suffer from numerous disadvantages.Firstly, when the grasped object is fragile, its gripping by a grab-likegripper may lead to its deformation. Moreover, before gripping anobject, it is necessary to accurately position the gripper with respectthereto. Furthermore, articulated grippers are complex equipment havingwearing parts, whilst also being relatively heavy and onerous.

The invention specifically relates to a gripper for transporting fragileobjects without any crushing risk, said gripper not having to beaccurately positioned with respect to the objects to be seized andhaving a particularly simple and inexpensive design, because it has nomoving parts.

According to the invention, this result is obtained by means of apneumatic gripper, characterized in that it comprises an approximatelyU-shaped support, whereof one end branch carries an ejection nozzleconnected to a compressed air source, the nozzle being oriented towardsthe intermediate branch of the support, in the vicinity of a bendconnecting said intermediate branch to the other end branch of thesupport, the latter being shaped in such a way as to channel thecompressed air ejected by the nozzle towards the end of the other endbranch.

In such a pneumatic gripper, the grasping of an object is brought aboutby means of the pressure differences created by the compressed air jetleaving the nozzle. Thus, such a gripper makes it possible to transportobjects having a limited weight without damaging them when they arefragile. Moreover, the gripper does not have to be accurately positionedwith respect to the object to be grasped, because the latter isautomatically attracted when the compressed air intake is open. Finally,it has no moving parts, so that it cannot become worn out and is alsolight, inexpensive and self-cleaning, because the compressed air jetensuring the necessary gripping automatically cleans the active surfaceof the support.

Preferably, the support has a plate which is laterally defined, on itsface turned towards the interior of the U and on either side of thebend, by two rails for guiding the compressed air ejected by the nozzle.

An embodiment of the invention is described in greater detailhereinafter relative to the drawings, wherein show:

FIG. 1 A perspective view of a pneumatic gripper according to theinvention.

FIGS. 2a & 2b Side views of the gripper of FIG. 1 respectivelyillustrating the approach of the object to be grasped by the gripper andthe actuation of the latter permitting the holding of said object.

As illustrated in FIG. 1, the pneumatic gripper according to theinvention has an approximately U-shaped, rigid support 10, which cane.g. be mounted on the end of the articulated arm of an automaton orrobot. The support 10 is constituted by a rectangular plate, e.g. madefrom metal or a plastics material and whose ends are bent atapproximately 90° with respect to the central part 10a of the plate, inorder to form two end branches 10b and 10c.

The end branch 10b of the support 10 carries an ejection nozzle 12connected by a flexible pipe 14 to a compressed air source 16. Theejection nozzle 12 has a threaded portion 12a, which traverses a holeformed in the centre of the branch 10b of the support and it is fixed tosaid branch by a nut 18 screwed onto the threaded portion 12a. However,the nozzle 12 can be fixed to branch 10b of the support by any othermeans without passing outside the scope of the invention.

The ejection nozzle 12 issues into the interior of the U formed by thesupport 10 and is located in the median plane of the latter and orientedtowards a bend 10d formed in support 10 at the intersection of branches10a and 10c. More specifically, the compressed air jet 20 leaving nozzle12 strikes the intermediate branch 10a in the vicinity of bend 10d.

In order to channel the compressed air jet 20 leaving the ejectionnozzle 12, the support 10 also has two side rails 22 located along thesides of the support 10 on the face of the latter turned towards theinterior of the U. Rails 22 extend on either side of the bend 10d overthe entire length of the end branch 10c and over most of the length ofthe intermediate branch 10a of the support. They ensure that acompressed air jet leaving the ejection nozzle 12 does not pass beyondthe sides of the support.

The rails 22 can be in one piece with the support 10, particularly whenthe latter is made from a moulded plastics material. They can also beconnected to the plate consituting the support 10, e.g. by bonding orwelding.

The use of the pneumatic gripper described hereinbefore with referenceto FIG. 1 will now be described in detail relative to FIGS. 2a and 2b.In order to grasp an object, whose profile is indicated at O in FIG. 2a,the pneumatic gripper is moved towards said object without anyparticular accuracy being required, in such a way that the object islocated in the vicinity of the face of support 10 turned towards theinterior of the U. This approach operation is illustrated by arrow F1 inFIG. 2a. During the gripper approach of the object, the compressed airsupply from nozzle 12 is interrupted.

As illustrated in mixed line in FIG. 2b, when the object O is in partencircled by the C-shaped support 10, the compressed air supply isopened, so that a compressed air jet is ejected by nozzle 12. Bearing inmind the orientation of the latter, the compressed air channelled byrails 22 follows an inwardly curved path at bend 10d along branch 10c.Thus, a pressure reduction or vacuum zone is created in the regionaround which the jet passes, in the vicinity of bend 10. The ejection ofcompressed air by nozzle 12 consequently has the effect of engaging theobject O with the rails 22 of the support in the vicinity of bend 10dand as illustrated by arrow F2 in FIG. 2b.

The position of object O when engaging against rails 22 under the effectof the compressed air jet from nozzle 12 is shown in continuous lineform in FIG. 2b. In this position, part of the compressed air jetcontinues to pass round the object O between the rails 22 (arrows FA),whilst another part of said jet strikes the object and then passesdirectly out of the support (arrows FB), which has the effect of helpingto maintain the object in the gripper. Under these conditions, theobject can be displaced in any direction with the aid of the gripper.

By giving the dimensions of the support 10 and the pressure of thecompressed air jet values appropriate for the dimensions and weight ofthe objects to be seized, it is possible to use the pneumatic gripperaccording to the invention for seizing objects having varied dimensionsand weights. In a non-limitative example, the depth of the U-shapedsupport 10 can be approximately 3 cm and the compressed air supplypressure approximately 6 bars.

Thus, tests have shown that a gripper according to the invention havingthe aforementioned characteristics makes it possible to raise andmanipulate full bottles with a weight exceeding 100 g, paperhandkerchiefs, stoppers, recording pens, nuts, etc.

Thus, the pneumatic gripper described hereinbefore makes it possible toseize or grasp objects having a random shape and a limited weight.Moreover, there is no need for an accurate positioning of the gripperwith respect to said objects. Moreover, in view of the fact that thegripper according to the invention has no moving parts, it does notbecome worn out and can be easily controlled. The gripper is also lightand inexpensive, whilst the compressed air jet bringing about thegripping action also ensures the self-cleaning of the support.

Obviously, the invention is not limited to the embodiment described inexemplified manner hereinbefore and in fact covers all variants thereof.In particular, the shape of the gripper support can differ slightly fromthat described hereinbefore. Thus, the inwardly curved part can have alarger radius. Instead of being produced in a planar plate, the supportcan have an approximately C-shaped section, whose opening is turnedtowards the interior of the U and whose edges fulfil the function ofchannelling the compressed air, as effected by rails 22 in the describedembodiment.

Moreover, the gripper can be placed on a randomly shaped robot and canalso be equipped with a handle permitting its direct handling by anoperator, e.g. in the case of particularly fragile objects or thosewhose direct handling by human operators can be dangerous (razor blades,etc.).

I claim:
 1. A pneumatic gripper, comprising a substantially U-shapedsupport including a plate having an intermediate branch and two endbranches, an ejection nozzle carried by a first of said end branches andconnected to a compressed air source, said ejection nozzle supplying acompressed air jet which strikes the intermediate branch in the vicinityof a bend formed in said plate, at the intersection of the intermediatebranch with a second of said end branches, jet guide means beingprovided on said plate to channel the compressed air jet from saidintermediate branch to an end of said second end branch opposite to saidbend.
 2. A pneumatic gripper according to claim 1, wherein said jetguide means comprise two rails provided on a face of said plate on whichissues said ejection nozzle, along lateral sides of said plate.
 3. Apneumatic gripper according to claim 1, wherein the end branches of theplate are bent at substantially 90° with respect to the intermediatebranch.